First of all, all the data in the computer are stored in bits (0 or 1), and the unit is called: bits;

Then, each 8-bit binary number (for example, 0 1 01) represents a byte size, that is,1byte =8 bits;

Then, each data type in C language has a fixed byte size. For example, the char type is a byte, that is, 8 bits, and the size of the int type is related to the machine word length of a specific computer cpu. If it is 16-bit cpu, it is 2 bytes = 16-bit cpu, and if it is 32-bit CPU, it is 4 bytes =32-bit CPU.

Finally, the value range of each data type is determined by its byte size. For example, the value range of the char type is-2 7 ~ 2 7-1(this involves the knowledge of the conversion between binary numbers and decimal numbers, so I won't say it here).